The present invention relates to a transport apparatus for perforated objects such as perforated circuit boards. More particularly, the present invention relates to a transport apparatus for removing perforated objects from a stack of such objects.
Frequently in the electronics industry, a circuit board must be removed from a stack of such boards and conveyed to a work station for further operations or installation. Automated devices are normally employed for this purpose. One type of automated device used for this purpose includes a vacuum operated gripper head which removes the top circuit board from the stack by means of suction. In the case of perforated circuit boards, however, difficulties often arise due to the tendency of such suction-operated gripper heads to lift more than one circuit board from the stack.
It is sometimes possible to reduce the tendency of the gripper head to lift more than one object by adjusting the suction power of the gripper head so that the weight of only a single circuit board will be supported. Adjustments of this type, however, must be highly accurate and, when possible, require expensive control devices Furthermore, the transport device would require delicate adjustment whenever the type of circuit board being transported is changed.
U.S. Pat. No. 3,602,543 issued Aug. 31, 1971, relates to a vacuum-operated lifting device for lifting cargo having a surface with a hole therethrough. Within a suction cup a plate is provided which overlies the hole, and, when the suction cup is applied to the cargo, the end plate causes a valve stem associated therewith to open a valve to a vacuum source. The plate has a check design of ribs forming a large number of open bottom chambers and a conduit leading form each chamber to the suction cup carrier The conduits are of such a size that they permit suction of those chambers closed by the end of the cargo and prevent large quantities of air from flowing through those conduits in communication with the cargo hole.
This device is suitable for use with loads having one, or a few, relatively large openings A device of this type, however, is not suitable for use with circuit boards which have a relatively large number of small perforations. Furthermore, a device of this type is difficult to construct properly and relatively expensive.
U.S. Pat. No. 2,841,433 relates to a vacuum-operated gripper device for lifting boxes, cartons, or the like from pallets or conveyor belts. A row of curtain-like flaps having sealing elements provided at their end portions is provided. This gripper, however, is not suitable for use with circuit boards.
Other gripper devices are disclosed, for example, in U.S. Pat. No. 3,523,707, Japanese Laid-Open Patent Publication No. 57-14723 and French Patent No. 2,184,072. Each of these gripper devices are divided into a plurality of chambers. A relatively complex distributor system is provided for the vacuum source to prevent excessive loss of suction due to openings in the object being moved. These grippers are quite complex and expensive, and are not well-suited for use in transporting perforated circuit boards.
The present invention is an improvement over previous suction-operated transport devices. More particularly, the present invention simply and economically overcomes the undesirable tendency of known transport devices of removing more than a single circuit board from the top of a stack of perforated circuit boards.